Check for stack space more intelligently.

libgcc sets the stack limit field in TCB to 256 bytes above the actual
allocated stack limit.  This means if the function's stack frame needs
less than 256 bytes, we can just compare the stack pointer with the
stack limit.  This should result in lesser calls to __morestack.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145766 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86FrameLowering.cpp b/lib/Target/X86/X86FrameLowering.cpp
index 182af84f7cac9cb89ecbf0682b10bd2443a3bdaa..27b762af69f07006e0da256ac7780a3e025245fc 100644 (file)
--- a/lib/Target/X86/X86FrameLowering.cpp
+++ b/lib/Target/X86/X86FrameLowering.cpp
@@ -1306,6 +1306,10 @@ GetScratchRegister(bool Is64Bit, const MachineFunction &MF) {
   }
 }
 
+// The stack limit in the TCB is set to this many bytes above the actual stack
+// limit.
+static const uint64_t kSplitStackAvailable = 256;
+
 void
 X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
   MachineBasicBlock &prologueMBB = MF.front();
@@ -1360,16 +1364,24 @@ X86FrameLowering::adjustForSegmentedStacks(MachineFunction &MF) const {
     TlsReg = X86::FS;
     TlsOffset = 0x70;
 
-    BuildMI(checkMBB, DL, TII.get(X86::LEA64r), ScratchReg).addReg(X86::RSP)
-      .addImm(0).addReg(0).addImm(-StackSize).addReg(0);
+    if (StackSize < kSplitStackAvailable)
+      ScratchReg = X86::RSP;
+    else
+      BuildMI(checkMBB, DL, TII.get(X86::LEA64r), ScratchReg).addReg(X86::RSP)
+        .addImm(0).addReg(0).addImm(-StackSize).addReg(0);
+
     BuildMI(checkMBB, DL, TII.get(X86::CMP64rm)).addReg(ScratchReg)
       .addReg(0).addImm(0).addReg(0).addImm(TlsOffset).addReg(TlsReg);
   } else {
     TlsReg = X86::GS;
     TlsOffset = 0x30;
 
-    BuildMI(checkMBB, DL, TII.get(X86::LEA32r), ScratchReg).addReg(X86::ESP)
-      .addImm(0).addReg(0).addImm(-StackSize).addReg(0);
+    if (StackSize < kSplitStackAvailable)
+      ScratchReg = X86::ESP;
+    else
+      BuildMI(checkMBB, DL, TII.get(X86::LEA32r), ScratchReg).addReg(X86::ESP)
+        .addImm(0).addReg(0).addImm(-StackSize).addReg(0);
+
     BuildMI(checkMBB, DL, TII.get(X86::CMP32rm)).addReg(ScratchReg)
       .addReg(0).addImm(0).addReg(0).addImm(TlsOffset).addReg(TlsReg);
   }

diff --git a/test/CodeGen/X86/segmented-stacks.ll b/test/CodeGen/X86/segmented-stacks.ll
index c28c31911d24aa83a41fd6fcf4455a31c6059a7b..4f529c119f050f2be9921b2d658fcdc2c4ae8a6a 100644 (file)
--- a/test/CodeGen/X86/segmented-stacks.ll
+++ b/test/CodeGen/X86/segmented-stacks.ll
@@ -20,8 +20,7 @@ false:
 
 ; X32:      test_basic:
 
-; X32:      leal -12(%esp), %ecx
-; X32-NEXT: cmpl %gs:48, %ecx
+; X32:      cmpl %gs:48, %esp
 
 ; X32:      pushl $4
 ; X32-NEXT: pushl $12
@@ -41,8 +40,7 @@ false:
 
 ; X64:      test_basic:
 
-; X64:      leaq -24(%rsp), %r11
-; X64-NEXT: cmpq %fs:112, %r11
+; X64:      cmpq %fs:112, %rsp
 
 ; X64:      movabsq $24, %r10
 ; X64-NEXT: movabsq $0, %r11
@@ -66,17 +64,14 @@ define i32 @test_nested(i32 * nest %closure, i32 %other) {
        %result = add i32 %other, %addend
        ret i32 %result
 
-; X32:      leal (%esp), %edx
-; X32-NEXT: cmpl %gs:48, %edx
-
+; X32:      cmpl %gs:48, %esp
 
 ; X32:      pushl $4
 ; X32-NEXT: pushl $0
 ; X32-NEXT: calll __morestack
 ; X32-NEXT: ret
 
-; X64:      leaq (%rsp), %r11
-; X64-NEXT: cmpq %fs:112, %r11
+; X64:      cmpq %fs:112, %rsp
 
 ; X64:      movq %r10, %rax
 ; X64-NEXT: movabsq $0, %r10
@@ -86,3 +81,26 @@ define i32 @test_nested(i32 * nest %closure, i32 %other) {
 ; X64-NEXT: movq %rax, %r10
 
 }
+
+define void @test_large() {
+        %mem = alloca i32, i32 10000
+        call void @dummy_use (i32* %mem, i32 0)
+        ret void
+
+; X32:      leal -40012(%esp), %ecx
+; X32-NEXT: cmpl %gs:48, %ecx
+
+; X32:      pushl $0
+; X32-NEXT: pushl $40012
+; X32-NEXT: calll __morestack
+; X32-NEXT: ret
+
+; X64:      leaq -40008(%rsp), %r11
+; X64-NEXT: cmpq %fs:112, %r11
+
+; X64:      movabsq $40008, %r10
+; X64-NEXT: movabsq $0, %r11
+; X64-NEXT: callq __morestack
+; X64-NEXT: ret
+
+}